Wheatstone Bridge

Formula

Description

The Wheatstone bridge is a measurement circuit consisting of four resistors in a diamond configuration, powered by a voltage source, with the output measured across the middle of the two voltage divider branches. When the bridge is balanced (R1/R2 = R3/R4), the output voltage is zero. Any imbalance produces an output voltage proportional to the difference. This makes it extremely sensitive to small resistance changes, which is why it is universally used with strain gauges, load cells, RTDs, and other resistive sensors. An instrumentation amplifier is typically used to amplify the small bridge output.

Variables

• Vout — Bridge output voltage (V)
• Vin — Bridge excitation voltage (V)
• R1, R2 — Resistors in one divider arm (Ω)
• R3, R4 — Resistors in the other divider arm (Ω)

Practical Notes

For maximum sensitivity, all four resistors should be similar in value. A quarter-bridge uses one active sensor and three fixed resistors. A half-bridge uses two active sensors (opposite arms) for 2x sensitivity and temperature compensation. A full-bridge uses four active sensors for 4x sensitivity and excellent temperature rejection. Bridge excitation can be AC for improved noise immunity.